There are centuries-old conventions for placement of musical symbols in printed sheet music, all of which are designed to ensure that the music is presented as clearly and unambiguously as possible to performers. The general principle is that no two symbols should be allowed to collide with each other, though there are important exceptions, such as musical notes, and symbols such as clefs and key signatures that collide with the stave on which they are positioned.
This general principle gives rise to hundreds of specific conventions concerning the placement of particular kinds of symbols. For example, lyric text should be positioned below the staff in a row across the width of system, as close as possible vertically to the notes to which they belong; text dynamics and hairpin lines should be aligned at the same vertical position relative to the stave above, below any low notes, and grouped such that if they are within a certain horizontal distance, they should be aligned together, so that the musician's eye can take them in at a single glance.
Other objects should be aligned down the score across multiple staves. For example, if several instruments all have a change of dynamic at the same rhythmic position, those dynamics should ideally be positioned at the same horizontal position on all staves, so that the conductor can take them all in at a single glance.
Creating scores that adhere to these conventions is a laborious and time-consuming process. It involves painstaking adjustment of individual objects in order to make the score as clear, pleasing to the eye, and unambiguous as possible. Music notation software in general is able to provide default positions for different types of objects. However, more than half the time creating a score is still consumed by manual adjustments of the musical objects.